Numerous prior art attempts have been made to provide seat cushions which are comfortable, stable, and able to avoid the development of pressure sores due to prolonged use. Providing a seat cushion which is comfortable, stable, and able to avoid pressure sores, is of particular importance to wheelchair bound individuals as those individuals spend extended periods of time on the cushion and, in many cases, are of poor heath (e.g., convalescents). Individuals who spend extended periods of time upon a wheelchair seat cushion and who are of poor heath are highly susceptible to decubitus ulcers. Moreover, convalescents and the like often have to be strapped into a wheelchair in order to prevent the individual from falling forward and out of the wheelchair. The straps used to prevent the individuals from falling forward are kept relatively tight to achieve their retention purpose. The straps are thus not only uncomfortable, but can also lead to the formation of sores in the area where the straps are in contact with the individual.
U.S. Pat. No. 4,753,480 to Morell features a pad assembly for wheelchairs which includes a high density base layer and two intermediate density layers stacked upon the high density layer. The two intermediate density layers include openings and a plurality of low density inserts for insertion in the openings. In an alternate embodiment, a continuous top layer is provided which is either of the same material as the underlying intermediate layer or formed of an impact foam which form fits to the buttocks of the cushion user. The cushion assembly includes an outer cover which holds the layers and inserts in position. The cushion assembly includes a variety of different low density inserts for use in varying situations. Mini-pads formed of the same material as the bottom pad are also provided to achieve posture correction in the cushion user. The multi-unit arrangement of Morell is subject to difficulty in manufacturing and user assembly. The arrangement and compression modulus value of the pads fails to optimize comfort. In addition, the various filler pad inserts and mini-pad inserts are subject to dislocation, incorrect arrangement and are easily lost or misplaced.
U.S. Pat. No. 4,960,304 to Frantz reveals another multi-layer wheelchair cushion. The cushion includes a high density bottom layer, a similar high density mass of foam material positioned so as to cover essentially the forward half of the bottom layer. The added mass of foam material includes an inclined portion and is covered by a lower Identification Force Deflection (IFD) value top layer of foam. Between the top layer and the bottom layer, and rearward of the added mass of foam, there is positioned a fluid filled bag in communication with a valve pump. The cushion is described as being adaptable to the configuration of the person through expulsion of some of the fluid in the bag following a person sitting on the cushion. Like the cushion assembly of Morell, Frantz presents a complex assembly with a multitude of components which can become easily lost or misplaced (e.g., the valve pump). Further, the conforming steps of the cushion to Frantz would require additional work on the already overburdened personnel caring for convalescents and the like.